Under a kitchen sink is a common place for mold. There is a lot of water coming in and out of that area and sometimes very minor leaks go undetected. Something very minor can still cause a big problem! What I personally do with my home is keep something under the kitchen sink that I need to use every day. This allows you to continually check the area for mold/water and you will be able to see it right away instead of a week/month(s) later. Luckily for this home we only had to remove a couple cabinets and some drywall. Which to most may seem like a lot but there are times that someone is getting a brand-new kitchen!